1. Field of the Invention
The present invention relates to the art of treating raw materials with a gaseous fluid in a thermal treatment stage, which sometimes may involve a chemical reaction. Maximum efficiency in the thermal exchange and the chemical reaction is obtained when the solid raw material is in contact with the gaseous fluid in a finely divided or pulverulent state. Accordingly, this invention relates more particularly to an apparatus for distributing pneumatically conveyed solid pulverulent material over an annular area of large diameter, and specifically to a vertical furnace for calcining solid pulverulent material, the furnace comprising a ceiling, a combustion chamber adjacent the ceiling and such an apparatus mounted on the furnace ceiling.
2. Description of the Prior Art
The invention is applicable most particularly to the calcination or pre-calcination of raw materials for the manufacture of cement clinker. Generally, vertical furnaces are used for this purpose. These furnaces conventionally have a symmetry of revolution and are equipped with one or more burners and means for introducing solid materials into the furnace and to disperse them in the hot combustion gases produced by the burner or burners. It is difficult to obtain a proper dispersion of the solid materials in the gas, particularly if the furnace has a large diameter, for example in excess of two meters. The points of introduction of the materials into the furnace may be multiplied but the equal distribution of a flow of hot solid materials between several inlets poses problems which have not been solved satisfactorily. It has also been proposed to introduce the solid materials in suspension in a flow of a gaseous fluid entering the furnace tangentially but this has the disadvantage of causing centrifuging of the solids and this, in turn, brings with it a granulometric segregation of the materials by particle size. Consequently, the particles are subjected to differences in treatment, depending on their size.
Finally, it has also been proposed to introduce the solid material into the furnace in suspension in a gas current of annular cross section, which surrounds the flame of the burner and whose principal direction of flow runs parallel to that of the gas constituting the flame. In this manner, a moving curtain of material is formed around the flame of the burner and its heat radiation is effectively used for treating the material. The highest effectiveness is attained when the material is distributed densely and uniformly around the flame, and the material curtain has a small width. However, any irregularity in the distribution creates a discontinuity in the material curtain and risks causing local overheating.